1 //===-- PeepholeOpts.cpp --------------------------------------------------===//
3 // Support for performing several peephole opts in one or a few passes over the
4 // machine code of a method.
6 //===----------------------------------------------------------------------===//
8 #include "llvm/CodeGen/PeepholeOpts.h"
9 #include "llvm/CodeGen/MachineFunction.h"
10 #include "llvm/CodeGen/MachineInstr.h"
11 #include "llvm/Target/TargetMachine.h"
12 #include "llvm/Target/TargetInstrInfo.h"
13 #include "llvm/Target/TargetOptInfo.h"
14 #include "llvm/BasicBlock.h"
15 #include "llvm/Pass.h"
17 //************************* Internal Functions *****************************/
20 DeleteInstruction(MachineBasicBlock& mvec,
21 MachineBasicBlock::iterator& BBI,
22 const TargetMachine& target) {
23 // Check if this instruction is in a delay slot of its predecessor.
24 if (BBI != mvec.begin()) {
25 const TargetInstrInfo& mii = target.getInstrInfo();
26 MachineInstr* predMI = *(BBI-1);
27 if (unsigned ndelay = mii.getNumDelaySlots(predMI->getOpCode())) {
28 // This instruction is in a delay slot of its predecessor, so
29 // replace it with a nop. By replacing in place, we save having
30 // to update the I-I maps.
32 assert(ndelay == 1 && "Not yet handling multiple-delay-slot targets");
33 (*BBI)->replace(mii.getNOPOpCode(), 0);
38 // The instruction is not in a delay slot, so we can simply erase it.
43 //******************* Individual Peephole Optimizations ********************/
46 RemoveUselessCopies(MachineBasicBlock& mvec,
47 MachineBasicBlock::iterator& BBI,
48 const TargetMachine& target) {
49 if (target.getOptInfo().IsUselessCopy(*BBI)) {
50 DeleteInstruction(mvec, BBI, target);
57 //************************ Class Implementations **************************/
59 class PeepholeOpts: public BasicBlockPass {
60 const TargetMachine ⌖
61 bool visit(MachineBasicBlock& mvec,
62 MachineBasicBlock::iterator BBI) const;
64 PeepholeOpts(const TargetMachine &T): target(T) { }
65 bool runOnBasicBlock(BasicBlock &BB); // apply this pass to each BB
66 virtual const char *getPassName() const { return "Peephole Optimization"; }
69 // Apply a list of peephole optimizations to this machine instruction
70 // within its local context. They are allowed to delete MI or any
71 // instruction before MI, but not
73 bool PeepholeOpts::visit(MachineBasicBlock& mvec,
74 MachineBasicBlock::iterator BBI) const {
75 /* Remove redundant copy instructions */
76 return RemoveUselessCopies(mvec, BBI, target);
80 bool PeepholeOpts::runOnBasicBlock(BasicBlock &BB) {
81 // Get the machine instructions for this BB
82 // FIXME: MachineBasicBlock::get() is deprecated, hence inlining the function
83 const Function *F = BB.getParent();
84 MachineFunction &MF = MachineFunction::get(F);
85 MachineBasicBlock *MBB = NULL;
86 for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I)
87 if (I->getBasicBlock() == &BB)
90 assert(MBB && "MachineBasicBlock object not found for specified block!");
91 MachineBasicBlock &mvec = *MBB;
93 // Iterate over all machine instructions in the BB
94 // Use a reverse iterator to allow deletion of MI or any instruction after it.
95 // Insertions or deletions *before* MI are not safe.
97 for (MachineBasicBlock::reverse_iterator RI=mvec.rbegin(),
98 RE=mvec.rend(); RI != RE; ) {
99 MachineBasicBlock::iterator BBI = RI.base()-1; // save before incr
100 ++RI; // pre-increment to delete MI or after it
108 //===----------------------------------------------------------------------===//
109 // createPeepholeOptsPass - Public entrypoint for peephole optimization
110 // and this file as a whole...
112 FunctionPass* createPeepholeOptsPass(TargetMachine &T) {
113 return new PeepholeOpts(T);